Thermoplastic starch compositions incorporating a particulate filler component

Abstract

Thermoplastic starch compositions that include a particulate filler, e.g. an inorganic filler component, and optional fibrous component The compositions include a thermoplastic phase comprising a thermoplastic starch melt that contains, at a minimum, starch blended with an appropriate plasticizing agent under conditions in order for the starch to form a thermoplastic melt. The thermoplastic phase may also include one or more additional thermoplastic polymers and other optional reactants, liquids or cross-linking agents to improve the water-resistance, strength, and / or other mechanical properties of the thermoplastic melt, particularly upon solidification. The inorganic filler component may affect the mechanical properties but will mainly be added to reduce the cost of the thermoplastic starch compositions by displacing a significant portion of the more expensive starch or starch / polymer melt. Fibers may optionally be included in order to improve the mechanical properties of the thermoplastic starch compositions. The thermoplastic starch compositions may be shaped into a wide variety of useful articles, such as sheets, films, containers, and packaging materials. Because the thermoplastic starch compositions will typically include a thermoplastic phase that is biodegradable, and because the other components will either constitute a naturally occurring mineral and optionally a natural fiber, the overall composition will typically be more environmentally friendly compared to conventional thermoplastic materials.

Description

1. The Field of the InventionThe present invention relates to compositions and methods for manufacturing thermoplastic starch compositions and articles made therefrom. More particularly, the present invention relates to thermoplastic starch compositions that include a particulate filler component. The thermoplastic starch compositions may optionally include one or more additional thermoplastic polymers blended therewith and fibers for reinforcement.2. The Relevant TechnologyA. Sheets, Containers, and Other Articles Made From Paper, Plastic, Glass and Metal.Materials such as paper, paperboard, plastic, polystyrene, and metals are presently used in enormous quantity as printed materials, labels, mats, and in the manufacture of other articles such as containers, separators, dividers, envelopes, lids, tops, cans, and other packaging materials. Advanced processing and packaging techniques presently allow an enormous variety of liquid and solid goods to be stored, packaged, or shipped whi...

AI Technical Summary

Benefits of technology

The raw material that is used to make the thermoplastic starch compositions of the present invention preferably comprises native, ungelatinized starch granules, although one or more starch derivatives may also be used, either alone or in combination with native starch. Native starch granules are made thermoplastic by mixing and heating in the presence of an appropriate plasticizer to form a starch melt The starch melt is then blended with on, or more non-starch materials in order to improve the properties and / or reduce the cost of the resulting thermoplastic starch composition. At a minimum, a particulate filler component is blended with the starch melt, preferably an inexpensive, naturally occurring mineral particulate filler ("inorganic filler"). In order to increase the tensile strength and other desirable mechanical properties of the starch / filler blend, other admixtures such as fibers, one or more synthetic polymers, cross-linking agents, softening agents, and the like may be included within the thermoplastic starch compositions.

Controlling the degree of crystallinity by means of controlling compositional as well as processing variables, may be helpful in engineering a final product having desired properties. On the one hand, solidified thermoplastic starch compositions that have lower crystallinity and which are more amorphous will generally have greater tensile strength, flexibility, bending endurance, and will behave like a wide variety of conventional thermoplastic polymers. On the other hand, such compositions will generally be more sensitive to heat over a wider range of temperatures. Thus, more highly crystalline thermoplastic compositions may be more suited for the manufacture of articles that need to be more heat-resistant, such as microwavable containers. Because more amorphous compositions tend to soften at lower temperatures due to such polymers having a wider softening range compared to crystalline polymers which have a more distinct melting point, they may have the tendency to soften when heated in a microwave oven. In contrast, compositions having a greater degree of crystallinity will tend to remain more rigid until heated to even higher temperatures and for longer periods of time compared to more amorphous polymers. The same is true for more amorphous polymers that are cooled to or below their glass transition temperature.

Problems solved by technology

However, in the case where a more volatile plasticizing solvent such as water is used, and where the melting point of the starch will cause the more volatile plasticizing solvent to rapidly vaporize, it may be necessary to maintain enough internal pressure, such as within an extruder barrel, to keep the plasticizer from violently expanding and impeding the process of forming the starch melt.